California company ships first batch of ‘world’s highest density’ batteries

Amprius, a California-based company, recently delivered the first batch of what it claims to be the most energy-dense lithium batteries on the market. By weight, these silicon anode cells carry 73% more energy than Tesla’s Model 3 cells, but take up 37% less space.

According to Enpower, Tesla’s current Model 3 cells carry around 260 Wh/kg and 730 Wh/l, making them a state-of-the-art comparable. However, the new Amprius cells are a significant step forward in terms of specific energy and energy density, with 450 Wh/kg and 1150 Wh/l respectively. And the company points out that the undisclosed number of cells it has delivered to “an industry leader in a new generation of high-altitude pseudo-satellites” gives it bragging rights to have “the cells highest energy density available in the battery industry today”. ”

The exceptional performance of higher density batteries, according to Amprius, is attributed to its silicon nanowire anode technology. Since electrons cannot move through the electrolyte or separator between cathode and anode – when you charge a lithium-ion battery – you are effectively picking an electron from each lithium atom sitting peacefully at the cathode and transport it through the anode via external wiring. Positively charged lithium ions are drawn through the electrolyte and separator by their negative charge. As a result, they each find an electron and implant into the graphite lattice at the anode.

According to Amprius, the silicon nanowire electrodes can store more lithium than a traditional graphite array, and they survive long enough to compete with current technology. (Credit: Amprius)

Amprius replaced the graphite network with silicon nanowires. Silicon can hold ten times more lithium than graphite, but it swells and cracks easily, reducing cell life. According to Amprius, when silicon is formed into porous nanowires arranged in a forest of shorter wires with longer wires between them, the silicon can support expansion and resist breakage, increasing cell life to the point where silicon anodes could become a competitive technology.

According to the company, because the silicon nanowires are embedded in the anode substrate, the conductivity (and therefore the power) is high. Additionally, he claims cell cycle life is “exceptional” and “continually improving”, but he gives no numbers and that the anode is the only part of the battery that changes; the rest can be made with existing production methods and components.

Amprius cells significantly outperform current lithium batteries in energy density by weight and volume
Amprius cells significantly outperform current lithium batteries in energy density by weight and volume. (Credit: Amprius)

The world is ready and waiting for next-generation battery cells capable of storing more energy in a smaller, lighter package. Everything from electric vehicles to smartphones would benefit from reduced space and weight. Additionally, emerging technologies such as VTOL electric aircraft desperately need batteries that can extend their range and capabilities.

Of course, specific energy and energy density are just two metrics a battery has to compete on. Charge/discharge rates, thermal performance, safety, lifespan and price will all play a role. The fact that Amprius’ initial customer is in high-tech aerospace and manufactures satellites suggests that these cells will not compete on price for the time being.

The company will soon select a location to begin construction of a large production plant, bringing economies of scale to make this technology relevant in the electric vehicle market and beyond.

Laura J. Boyer